The invention relates to the field of digital signal processing and in particular to determining a measure for a signal change and a corresponding method of phase control.
Gradient detection for phase control is implemented using a continuous measuring circuit, for example, an operational amplifier wired as a differentiator. A gain adjustment may be implemented following the differentiator, followed by an analog-to-digital converter (ADC) that digitizes the gradient information at a given point in time.
The signal path is, however, continuously under load by a frequency-dependent current flow. In addition, an integrated circuit to implement this operation becomes expensive due to an increased surface-area and power requirement. The phase response of a corresponding sensor circuit must be known and must accordingly be taken into account during the phase control.
Phase control may be performed several different ways. In a first approach, a multiple sampling per pixel period is implemented. The disadvantage here is that, particularly in the case of fast sampling in the signal path, an additional increase in the sampling rate can result in a significant reduction in the resolution of the analog-to-digital converters, and can excessively increase the power drain of these converters.
In a second approach, a transmission is effected with an additional reference signal with a known curve or a known pixel frequency. However, an additional reference signal with a known curve or a known pixel frequency is not available for all applications and may entail a significant additional technical cost.
In a third approach, phase control is effected using statistical techniques, for example, by maximizing the average difference between two successive sampling values. It is possible for large latency times to occur which are critical specifically in regard to moving images. In addition, it may not be possible to correct a phase drift quickly enough.
In a fourth approach according to published German Patent Application DE 10 2004 027 093, a method is described in which digitized gradient values and sampling values are utilized to estimate the phase position of a steady-state signal segment. In this approach, the quality of the control algorithm is a function of the signal curve. If this signal curve deviates from a sinusoidal shape, the control algorithm may no longer operate efficiently.
What is needed is an improved device to determine a measure for a signal change and an improved method to effect phase control.